The present invention relates to a pillar intended to form part of a furniture support or another piece of furniture equipped with a gas spring.
For a long time seats have been known which are equipped with gas springs and which are composed of the following parts:
a foot resting on the floor,
a top part constituting the seating surface in the case of a seat interposed between the foot and the top part, and
a substantially vertical central barrel called a "pillar", which is telescopic and adjustable in height.
In the present text references to position, such as "vertical", "top" and other expressions, relate to the situation occurring when the seat or other piece of furniture is in the position of use.
The seat pillar is in turn composed of three parts:
a bottom tube or "support tube" fastened to the foot, PA1 a top sliding tube fastened to the top part of the piece of furniture, and PA1 a lockable gas spring mounted inside the sliding tube and acting between the two tubes. PA1 at the top by a stop means bearing against the inside surface of the cone and provided with a vertical through passage in which an axial pushrod intended for operating the control finger can move; PA1 at the bottom by a detachable stop means provided with a vertical through passage in which the piston rod of the gas spring is movable.
The gas spring balances the weight of the top part and serves to adjust the length of the pillar, and therefore to maintain the height selected for the top part. Its body is placed, with lateral clearance, in the sliding tube and its rod is fixed by its end remote from the piston on the bottom of the support tube. At its end remote from the rod the body carries an axially movable locking control finger.
The seating surface of the seat is equipped with a pivotable device enabling the control finger to be operated.
The pillar, inside which the gas spring has been placed, is often in the form of a unit delivered ready for use to the furniture manufacturer, who has simply to fasten it to the support and to the seating surface.
For this purpose the foot and the seating surface are each provided with a part in the form of a hollow cone, and the ends of the pillar, that is to say the ends of the support tube and of the sliding tube, have a corresponding matching conical shape for force fitting.
The gas spring body placed inside the sliding tube is held axially:
An arrangement of this kind is described, for example, in German Utility Model No. 84.17962. According to the latter the top stop means is a frustoconical component of a material less rigid than that of the sliding tube.
Pillars of this kind generally give satisfaction and have a long life. Nevertheless, improvements are still possible.
The present invention seeks to provide a pillar for seats, which has a lengthened life without any substantial increase in the weight and the cost price of this pillar.
A systematic study of the causes of failures of existing pillars has shown that such failures occur most often at or near the conical end part of the sliding tube.
Without any wish to analyze here all the possible causes of this preferential location of failures, which may be numerous, it appeared to the inventor to be necessary to reinforce the pillar in that region.
An increase of the thickness of the metal of the sliding tube might have been contemplated. This would entail increased consumption of material and make it more difficult to form the conical part. In addition, as the outside diameter is dictated by the shape of the seating surface, it would have been necessary to reduce the inside diameter, and consequently also to reduce the diameter of the gas spring, which might then have become inadequate.